Studies will be continued on the conversion and inactivation of selected neuropeptides by purified brain enzymes. Examples include cathepsin B purified from brain and pituitary, and a dipeptidyl carboxypeptidase (angiotensin converting enzyme). Cathepsin B will be incubated with 125I or 35-methionine labeled beta-endorphin (LPH 61-91), beta-LPH (LPH 1-91), the 31K common precursor of beta-LPH and ACTH, and rate of degradation monitored by slab-gel SDS-acrylamide electrophoresis, by the use of HPLC or conventional peptide mapping procedures. In addition, other catheptic B-like enzymes hydrolyzing Bz-Arg-Nap will be studied in terms of cleavage of opiate peptides, hypothalamic releasing factors and substance P. Dipepticyl carboxypeptidase purified by immunoaffinity chromatography will be further characterised in terms of its specificity, molecular weight, and effects of naturally occurring and synthetic inhibitors. Membrane bound forms of this enzyme will be separated by ion exchange to determine if a specific angiotensin converting enzyme can be separated from one inactivating enkephalin (enkephalinase) by removal of the C-termal dipeptide. The specificity of dipeptidyl carboxypeptidase will be examined in detail using substrate P and intermediate sized endorphins and enkephalin analogs having enhanced in vivo activities.